(1) Field of the Invention
This invention relates to a webbing retractor suitable for use with a vehicle seat belt, and more particularly to such a webbing retractor that is durable against high tensile forces which may be applied to the webbing in the event of emergencies.
(2) Description of the Prior Art
Webbing retractors of the type as shown in FIGS. 1(a) and 1(b) have found wide-spread commercial utility for seat belts in recent years. Namely, a take-up spindle 3 carrying a cogwheel 2 provided thereon and a lock lever 4 are inserted in a casing 1 from the outside (i.e., in the direction indicated by X in the figure). Then, a webbing W of a desired color is inserted through a slot 5 of the take-up spindle 3 and a slip-off preventive bar 7 is caused to extend through a looped end portion 6 so as to fasten the webbing W on the take-up spindle 3. In the event of an emergency such as a vehicle collision or the like, a sensor mechanism 8 is actuated to bring a pawl 9 of the lock lever 4 into engagement with the cogwheel 2, thereby inhibiting the take-up spindle 3 from any further rotation and preventing any further release of the webbing W.
However, webbing retractors of the above sort involve a possible danger that, because the cogwheel 2 and the pawl 9 of the lock lever 4--which pawl 9 is engageable with the cogwheel 2--are located outside a side plate 10 of the casing 1, the lock lever 4 and cogwheel 2 are held together only at their proximal ends just like cantilevers and they may undergo deformation and may eventually be disengaged when an extremely heavy load is exerted in the event of an emergency or the like. Furthermore, the side plate 10 defines a relatively large hole 11 so as to permit the take-up spindle 3 to extend therethrough. Provision of such a hole has reduced the strength of the casing 1, resulting in another possible danger that the casing 1 might be deformed under the influence of even a small load.
A variety of exemplary structural failures are schematically illustrated in FIGS. 2 through 6. FIG. 2 illustrates the take-up spindle 3 pulled in the upper right direction. Both side plates of the casing 1 have been deformed and are now aligned in the pulled direction. This has pushed the cogwheel 2 outwardly, leading to disengagement of the cogwheel 2 from the lock lever 4.
FIG. 3(a) illustrates the directions of forces produced when the rotation of the cogwheel 2 in the direction indicated by A has been restrained. The take-up spindle 3 is subjected to a force exerted in the direction indicated by B while the lock lever 4 is exerted by a force in the direction shown by C. In FIG. 3(b), the hole 11 has been deformed into an elongated hole due to the application of the force in the direction indicated by B and the take-up spindle 3 has been allowed to move in the upper right direction, resulting in disengagement of the cogwheel 2 from the lock lever 4. Incidentally, such a movement of the take-up spindle can be positively utilized to construct an emergency locking mechanism as disclosed, for example, in U.S. Pat. No. 4,101,094 issued July 18, 1978 to Wallin and U.S. Pat. No. 4,350,313 issued Sept. 21, 1982 to Adomeit, although the structure of such an emergency locking mechanism is obviously different from the structure shown in FIG. 3(b). In FIG. 3(c), the lock lever 4 has been shifted in the lower left direction due to the application of the force in the direction indicated by C, also resulting in disengagement of the cogwheel 2 from the lock lever 4. Incidentally, U.S. Pat. No. 3,960,339 issued June 1, 1976 to Fisher discloses a retractor making, on the contrary, effective use of such a movement of the lock lever.
FIG. 4 illustrates an outwardly-bent cogwheel 2. In FIG. 5, the pawl 9 of the lock lever 4 has been bent downwardly. In these examples of deformation, the point of engagement between the cogwheel 2 and the pawl 9 of the lock lever 4 is progressively shifted away from the side plate 10 once the deformation starts and the deformation is thus promoted further as the bending moment becomes greater.
In addition, FIG. 6 illustrates a lock lever 4 in which the pawl 9 has been deformed in the rotary direction of the cogwheel because the pawl 9 was subjected to a rotary force produced at the take-up spindle.
If any one of the above types of disengagement takes place, the take-up spindle is caused to rotate and the webbing is thus paid out, thereby failing to protect the occupant safely.